Radio aerial system, and particularly directive aerial system



Dec. 5, 1950 w. JOHNSON 2,532,920 RADIO AERIAL SYSTEM, AND PARTICULARLY DIRECTIVE AERIAL SYSTEMS Filed Aug. 15, 1948 I Izventor WILLIAM A. JOHN 0 H Attorneys Patented Dec. 5, 1950 UNITED STATES Q'FFECE RADIO AERIAL SYSTEM, AND PARTICU- LARLY DIRECTIVE AERIAL SYSTEM William Arthur Johnson, Farnborcugh, England 6 Claims. 1

This invention relates to radio aerial systems which are of a directive character, and are sometimes referred to as omni-range beacons, for very high frequency radio communication and signalling.

An object of the invention is to provide a directive pattern of radiationpolarised in the plane of thepattern (normally the horizontal plane).

Another object of the invention is to provide a rotating horizontally polarised directive pattern such that the signal received at a fixed station is amplitude modulated substantially sinusoidally.

The invention consists essentially in the combination effectively in the same plane of a fed loop aerial and a parasitic dipole so as to produce in said plane the required directive pattern.

An aerial system in accordance with the invention comprises a fed loop aerial adapted for mounting in a horizontal plane and a parasitic dipole excitable by the loop disposed parallel with a chord of the loop in an adjacent horizontal plane.

The dipole may be mounted for rotation about the central vertical axis of the loop so that the directive pattern is caused to rotate and is preferably adjustably mounted relatively to said axis so as to enable its excitation and the degree of directivity of the pattern to be varied.

The feeders to the loop, of which there may be,

say, four pairs each pair feeding a quadrant of the loop so as to obtain substantially constant current distribution in the loop, preferably subtend an angle of approximately 45 with the plane of the loop so as to minimise both vertically polarised radiation from the feeders and interference effects between the feeders and the dipole.

The accompanying drawing is a perspective view of one practical embodiment of the invention which is shown and will now be described purely by way of example.

The loop I consists of four metal quadrants la-ld connected together to form a circle and supported by four radial arm 2 of insulating material.

Arms 2 project from a column 3 the head 4 of which isadjustably secured to the underside of a beam 5 by means of a hollow bolt 6 which is eccentric with the column 3 and passes through a slot 1 in the beam. A feed cable 8 passes through the bolt into the column head 4 which is hollow and constitutes a junction box for the four pairs of feeders 9 which extend at approximately 45 from the head 4 to the loop I.

Vertically below the centre of the loop I is a hollow pedestal 10 for a vertical shaft H, the

upper enlarged end [2 of which carries insulating radial arms 53 perforated for the adjustable mounting of a dipole M. A weight [5 also adjustably mounted on an arm I6 is arranged to balance the dipole about the vertical axis. The shaft H is driven by an electric motor (not shown) mounted below the pedestal Ill.

The polar diagram of radiation from the,loop in the horizontal plane is a circle and that of the dipole is a figure of eight so that the resultant is more or less a cardioid depending on the degree of excitation of the dipole. When the dipole is on a diameter of the loop the excitation is zero but increases as the dipole is moved towards the circumference to constitute a chord of the loop.

The above described embodiment of the invention is designed for use in connection with the omni-directional radio beacon (O. R. B.) described in U. K. Technical Paper No. 13 of the Provisional International Civil Aviation Organisation (P. I. C. A. O.) and. as such operates on a wavelength of about in. in the 100-156 mos. band. Typical dimensions of the embodiment for use on this wavelength are as follows:

Loop diameter 28 in. i. e. approximately wavelength.

Length of dipole 41 in. i. e. approximately wavelength.

Vertical spacing dipole and loop 10 in.

Dipole offset from loop 6 in.

The invention as above exemplified provides a directive pattern of horizontally polarised radiation in the horizontal plane and at low angles of elevation. At high angles of elevation (reaching a maximum at 45) a vertically polarised component due to the dipole is present and therefore if only horizontally polarised radiation is required to be received from the aerial system of the invention at high angles a means of suppressing the vertical component radiated at the higher angles must be provided. One suitable means is described in the specification accompanying my co-pending U. S. patent application Serial No. 44,185, filed August 13, 1948.

The construction described and shown is but one example of many practical forms the invention may take.

It may sometimes be desirable when carrying out the invention to incorporate means for adjusting some or all of the dimensions which have been shown as fixed. For example, the phase of the current in the dipole varies with its length and therefore may be made controllable within limits, by providing a telescopic or other extend- 3 ing form of dipole. Alternatively, or in addition, tuning means such as a variable capacity may be associated with the dipole. Provision could also be made for varying the diameter of the loop.

Complex radiation patterns may be produced according to the invention by providing more than one parasitic dipole excited by a single loop.

The amount of vertical spacing between the loop and the dipole depends upon the uniformity of the current in the loop. If dipole is placed too close the unavoidable irregularities in the field of the loop at the junction of the quadrants cause non-uniform excitation of the dipole as it rotates. For any particular construction there is an optimum spacing readily found by trial (10 in. in the example described above) at which the excitation is made practically uniform without serious loss of coupling.

I claim:

' 1. The combination in adjacent parallel planes of a fed loop aerial and at least one parasitic dipole disposed such that its projection on the plane of the loop contains a chord of the loop thereby producing in said plane of the loop a directive pattern of radiation polarised in said plane.

2. An erial system particularly for transmitting a horizontally polarized directive pattern of radiation comprising a fed loop aerial adapted for mounting in a horizontal plane and a parasitic dipole excitable by the loop disposed horizontally and such that its projection on the plane of the loop contains a chord of the loop.

3. An aerial system for transmitting a horizontall polarised directive pattern of radiation comprising a circular loop aerial, means for mounting said aerial horizontally, feeders for supplying high frequency current to said aerial, a

parasitic dipole and means rotatable about the central vertical axis of the loop aerial for sup porting the dipole horizontally and such that its projection on the plane of the loop contains a chord of the loop aerial.

4. An aerial system as claimed in claim 3 wherein the means for supporting said dipole are adjustable in respect of the distances of the dipole from said axis.

5. An aerial system for transmitting a horizontally polarised directive pattern of radiation comprising a circular loop aerial consisting of four quadrants, radial arms of insulating material for supporting said quadrants in a horizontal plane, a pair of' feeders extending substantially from the central vertical axis of the loop at an angle of approximately 45 to said axis to each quadrant, a parasitic dipole, and means rotatable about said axis for supporting the dipole close to and parallel to a chord of the loop aerial.

6. An aerial system as claimed in claim 5 wherein the means for supporting said dipole are adjustable in respect of the distance of the dipole from said axis.

WILLIAM ARTHUR JOHNSON.

REFERENCES CITED Ihe following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,054,896 Dallenbach Sept. 22, 1936 2,297,427 Neidhardt Sept. 29, 1942 2,391,026 McGuigan Dec. 8, 1945 2,408,825 Varian et a1. Oct. 8, 1946 FOREIGN PATENTS Number Country Date 96,462 Austria Mar. 26, 1924 

